JP4673514B2 - GaN compound semiconductor crystal manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a GaN-based compound semiconductor crystal used for manufacturing a semiconductor device such as a light-emitting device or an electronic device.
[0002]
[Prior art]
GaN-based compound semiconductors such as GaN, InGaN, AlGaN, InGaAlN (In _x Ga _y Al _1-xy N where 0 ≦ x, y; x + y ≦ 1) are materials for semiconductor electronic devices such as light-emitting devices and power devices In addition, it is attracting attention as a material that can be applied in various other fields.
[0003]
Conventionally, since it has been difficult to grow a bulk crystal of a GaN-based compound semiconductor, a substrate in which a thin-film single crystal such as GaN is formed by heteroepitaxy on a heterogeneous crystal such as sapphire is used for the electronic device. It was.
[0004]
However, since sapphire crystal and GaN compound semiconductor crystal have large lattice mismatch, there is a problem in that dislocation density of GaN compound semiconductor crystal grown on sapphire crystal increases and crystal defects occur. . Furthermore, since sapphire has a low thermal conductivity and is difficult to dissipate heat, there is a problem that when a substrate on which a GaN-based compound semiconductor crystal is grown on a sapphire crystal is used for an electronic device with high power consumption, the temperature tends to increase.
[0005]
Attempts have also been made to grow GaN-based compound semiconductor crystals by an ELO (Epitaxial Lateral Overgrowth) method using hydride vapor phase epitaxy (hereinafter abbreviated as HVPE). Here, the ELO method is, for example, forming an insulating film as a mask on a sapphire substrate, providing an opening in a part of the insulating film and using the insulating film as a mask, and exposing the exposed sapphire substrate surface as a seed for epitaxial growth. As a method for growing a highly crystalline GaN-based compound semiconductor crystal.
[0006]
According to this method, since the growth of the GaN-based compound semiconductor crystal starts from the surface of the sapphire substrate inside the opening provided in the mask and the growth layer spreads on the mask, the dislocation density in the crystal can be kept small. A GaN compound semiconductor crystal with few crystal defects can be obtained.
[0007]
However, since the GaN compound semiconductor crystal obtained by the ELO method has a large thermal strain, polishing is performed after the growth of the GaN crystal by the ELO method to separate the sapphire substrate to obtain a single GaN compound semiconductor crystal wafer. Then, there was a problem that the wafer was bent due to residual strain.
[0008]
Therefore, the present inventors use rare earth 13 (3B) group perovskite crystal as one of the materials of the different crystal substrate, and the GaN-based compound semiconductor by heteroepitaxy using the {011} plane or {101} plane as a growth plane. A method of growing was proposed (WO95 / 27815). Here, the {011} plane or {101} plane represents a set of planes equivalent to the (011) plane and the (101) plane, respectively.
[0009]
According to the growth technique of the prior application, for example, when NdGaO ₃ which is one of rare earth 13 (3B) group perovskites is used as a substrate and GaN is grown on the {011} plane or the {101} plane, the lattice mismatch is It is about 1.2%, and the lattice mismatch is extremely smaller than that in the case of using sapphire or SiC used as a substitute for the substrate. Therefore, since the dislocation density in the crystal is low, a GaN-based compound semiconductor crystal with few crystal defects can be grown.
[0010]
In addition, the prior application technique is further improved to form a first GaN layer on an NdGaO ₃ substrate at a low temperature (400 to 750 ° C.), and then to a predetermined temperature in an inert gas (N ₂ gas) atmosphere. There has been proposed an invention in which a second GaN layer is grown at a high temperature (800 to 1200 ° C.) on the first GaN layer by performing a heat treatment by raising the temperature (Japanese Patent Laid-Open No. 2000-4045). . This technique, since the NdGaO ₃ substrate can be prevented from being reduced by reaction with NH ₃ or the like in GaN-based compound semiconductor growth temperature (800 to 1200 ° C.), was grown due to the NdGaO ₃ substrate is reduced Degradation of the GaN crystal can be avoided.
[0011]
[Problems to be solved by the invention]
However, in the prior application technique (Japanese Patent Laid-Open No. 2000-4045), since the GaN thin film is formed by the hydride VPE method having a relatively high growth rate, it is difficult to control the thickness of the GaN thin film. Variation in film thickness increases. Moreover, since the GaN thin film is formed at a considerably lower temperature (400 to 750 ° C.) than the growth temperature (800 to 1200 ° C.) of the GaN-based compound semiconductor crystal so that the NdGaO ₃ substrate is not reduced, the crystal quality is poor.
[0012]
For this reason, the NdGaO ₃ substrate can be prevented from being reduced at the growth temperature of the GaN crystal by the above-described method, but the GaN thin film has an adverse effect on the GaN-based compound semiconductor crystal grown thereon, and The crystal quality may be degraded.
[0013]
The present invention relates to a method for producing a GaN-based compound semiconductor crystal using a rare earth 13 (3B) group perovskite as a substrate, by improving the quality of the GaN thin film formed between the substrate and the GaN-based compound semiconductor crystal. An object is to provide a technique for improving the crystal quality of a compound semiconductor crystal.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for growing a GaN-based compound semiconductor crystal on the surface (one main surface) of a rare earth 13 (3B) group perovskite crystal containing one or more rare earth elements as a substrate. in, by introducing on the substrate in the Ga atoms evaporated by heating the Ga raw material N ₂ gas, adsorbing the Ga atoms in the rare earth 13 (3B) group perovskite crystal substrate, subsequently, adsorbed forming a GaN thin film by nitriding the Ga atoms, further followed, a step of growing a GaN based compound semiconductor crystal on the GaN thin film, in which so as to have at least a.
[0015]
Thereby, since the GaN thin film can be formed with a uniform thickness, the GaN thin film does not adversely affect the quality of the GaN-based compound semiconductor crystal grown thereon, and the crystal quality is improved. In addition, the formation of the GaN thin film can prevent the substrate from being reduced at the growth temperature of the GaN-based compound semiconductor crystal.
[0016]
Desirably, in the step of adsorbing Ga atoms on the rare earth 13 (3B) group perovskite crystal substrate, the temperature of the Ga raw material should be lower than the temperature of the substrate in the range of 0.5 to 5 ° C. Thereby, Ga atoms can be efficiently adsorbed on the substrate, and the thickness of the adsorbed layer of GaN atoms can be controlled relatively easily.
[0017]
Further, by adsorbing the Ga atoms to the substrate with a thickness of one molecular layer to several molecular layers, it becomes possible to nitride all of the adsorbed Ga atoms, and the thickness of one molecular layer to several molecular layers is formed on the substrate. A GaN thin film is formed. Therefore, although the GaN thin film is formed at a temperature lower than the crystal growth temperature, the crystal quality of the GaN thin film is not significantly reduced. Thus, by improving the crystal quality of the GaN thin film, the crystal quality of the GaN-based compound semiconductor crystal grown on the GaN thin film can be improved.
[0018]
Further, the present invention can be applied to the case where a rare earth 13 (3B) group perovskite crystal containing at least one of Al, Ga and In as the 13 (3B) group element, for example, NdGaO ₃ crystal is used as a substrate.
[0019]
The process that led to the completion of the present invention will be described below.
Initially, the present inventors have grown a GaN-based compound semiconductor crystal according to the method for growing a GaN-based compound semiconductor crystal proposed in the previous application (Japanese Patent Laid-Open No. 2000-4045). I realized there was something going wrong. Therefore, in order to elucidate the cause of the deterioration of crystal quality, the crystal growth method of the prior application was studied repeatedly.
[0020]
In the crystal growth method of the prior application, after the substrate is mirror-polished and cleaned, the substrate is placed at a predetermined site in the hydride VPE apparatus, and the substrate temperature is raised to 600 ° C. while introducing N ₂ gas. A GaN thin film of about 100 nm is formed by heating and supplying GaCl generated from Ga metal and HCl gas and NH ₃ gas onto the NdGaO ₃ substrate using N ₂ carrier gas. Subsequently, the substrate temperature was raised to 1000 ° C. in an atmosphere of N ₂ gas as an inert gas, and then a GaN-based compound semiconductor crystal was grown on the GaN thin film.
[0021]
However, when the method of the prior application is applied, the hydride VPE method has a relatively high growth rate, so it is difficult to uniformly control the thickness of the GaN thin film, and the film thickness of the formed GaN thin film varies. I found it to happen. Further, since the GaN thin film is formed at a temperature (620 ° C.) considerably lower than the growth temperature (1000 ° C.) of the GaN-based compound semiconductor crystal so that the NdGaO ₃ substrate is not reduced, it is expected that the crystal quality is deteriorated. did it.
[0022]
Therefore, the present inventors have been able to prevent the NdGaO ₃ substrate from being reduced at the crystal growth temperature, while growing the GaN thin film formed according to the method of the prior application on the GaN thin film. We thought that the crystal quality of GaN-based compound semiconductor crystals may be degraded.
[0023]
And when a thicker GaN thin film was grown, the quality of the GaN compound semiconductor crystal was degraded, so the GaN thin film with poor and non-uniform crystal quality was grown on it. Has been found to affect. From this, it was convinced that by making the film thickness of the GaN thin film formed on the substrate uniform, the crystal quality of the GaN-based compound semiconductor crystal grown thereon can be further improved.
[0024]
Based on the above findings, the present inventors have intensively studied on a method for uniformly forming a GaN thin film on a rare earth 13 (3B) group perovskite crystal substrate, and as a result, the present invention has been completed.
[0025]
Specifically, by performing a process of adsorbing Ga atoms on the rare earth 13 (3B) group perovskite crystal substrate and a process of nitriding the adsorbed Ga atoms with NH ₃ or the like, the GaN thin film can be formed with a uniform thickness. Could be formed. As a result of Auger analysis of the sample after performing the above two steps, it was confirmed that GaN was formed on the substrate because an N peak was observed in addition to a Ga peak.
[0026]
As described above, the present invention has been found by an experiment for growing a GaN compound semiconductor crystal on an NdGaO ₃ substrate. In addition to a GaN compound semiconductor crystal, a GaN-based compound semiconductor crystal such as InGaN or AlGaN can be used. The same effect can be obtained when grown. As the rare earth 13 (3B) group perovskite crystal substrate, NdAlO ₃ , NdInO ₃ or the like can be used in addition to NdGaO ₃ .
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described in the case of growing a GaN compound semiconductor crystal using an NdGaO ₃ crystal as a substrate. In this embodiment, a substrate for crystal growth is formed by slicing an NdGaO ₃ ingot. At this time, the NdGaO ₃ substrate had a diameter of 50 mm and a thickness of 0.5 mm.
[0028]
(Example)
A method of forming a GaN thin film on an NdGaO ₃ substrate by applying the present invention and growing a GaN compound semiconductor crystal thereon will be described.
First, the mirror-polished NdGaO ₃ substrate was subjected to ultrasonic cleaning in acetone for 5 minutes, followed by ultrasonic cleaning with methanol for 5 minutes. After that, it was blown with N ₂ gas to blow off the droplets and then naturally dried. Next, the cleaned NdGaO ₃ substrate was etched with a sulfuric acid-based etchant (phosphoric acid: sulfuric acid = 1: 3, 80 ° C.) for 5 minutes.
[0029]
Next, after placing the NdGaO ₃ substrate at a predetermined site in the hydride VPE apparatus, the substrate temperature was raised to 724 ° C. while introducing N ₂ gas. Thereafter, the Ga raw material was heated to 722 ° C. at a position 1.2 m away from the substrate, and evaporated Ga atoms were supplied onto the substrate while N ₂ gas was introduced at 2000 sccm, thereby adsorbing Ga atoms on the substrate surface. .
[0030]
In this example, Ga atoms were supplied onto the substrate while maintaining this state for 15 minutes. Here, since the time for supplying one atomic layer of Ga atoms based on the evaporation rate of Ga at 722 ° C. is 150 seconds, in this embodiment, six atomic layers of Ga atoms are supplied. become. From this, it is considered that the film thickness of Ga atoms adsorbed on the substrate becomes a thickness corresponding to several atomic layers.
[0031]
Next, NH ₃ gas was supplied onto the substrate at 1000 sccm for 30 minutes, and Ga atoms adsorbed on the substrate were nitrided to form a GaN thin film. In this example, the thickness of the Ga atoms to be adsorbed on the substrate is very thin, such as several atomic layers, so that all the adsorbed Ga atoms can be nitrided, and a high-quality GaN thin film with a uniform film thickness can be obtained. Can be formed.
[0032]
Next, the substrate temperature was raised to 1000 ° C., and GaCl generated from Ga metal and HCl gas and NH ₃ gas were supplied onto the NdGaO ₃ substrate using N ₂ carrier gas. At this time, the growth rate is about 40 μm / h while controlling the amount of each gas introduced so that the GaCl partial pressure is 5.0 × 10 ⁻³ atm and the NH ₃ partial pressure is 3.0 × 10 ⁻¹ atm. A GaN compound semiconductor crystal was grown for 300 minutes.
[0033]
Thereafter, it was cooled at a cooling rate of 5.3 ° C./min for 90 minutes to obtain a GaN compound semiconductor crystal having a film thickness of about 200 μm.
The obtained GaN compound semiconductor crystal had an X-ray rocking curve half width (FWHM) of 100 seconds and was confirmed to have excellent crystal quality.
[0034]
(Comparative example)
Next, as a comparative example, a method of forming a GaN thin film on a NdGaO ₃ substrate by a conventional method and growing a GaN compound semiconductor crystal thereon will be described.
The comparative example was different from the above example only in the formation method of the GaN thin film, and the pretreatment of the NdGaO ₃ substrate, the growth conditions of the GaN compound semiconductor crystal, and the like were the same as in the example.
[0035]
First, the mirror-polished NdGaO ₃ substrate was subjected to ultrasonic cleaning in acetone for 5 minutes, followed by ultrasonic cleaning with methanol for 5 minutes. After that, it was blown with N ₂ gas to blow off the droplets and then naturally dried. Next, the cleaned NdGaO ₃ substrate was etched with a sulfuric acid-based etchant (phosphoric acid: sulfuric acid = 1: 3, 80 ° C.) for 5 minutes.
[0036]
Next, after this NdGaO ₃ substrate is placed at a predetermined site in the hydride VPE apparatus, the substrate temperature is raised to 620 ° C. while introducing N ₂ gas, and GaCl generated from Ga metal and HCl gas, NH ₃ gas was supplied onto the NdGaO ₃ substrate using N ₂ carrier gas to form a GaN thin film of about 100 nm.
[0037]
Next, the substrate temperature was raised to 1000 ° C., and GaCl generated from Ga metal and HCl gas and NH ₃ gas were supplied onto the NdGaO ₃ substrate using N ₂ carrier gas. At this time, the growth rate is about 40 μm / h while controlling the amount of each gas introduced so that the GaCl partial pressure is 5.0 × 10 ⁻³ atm and the NH ₃ partial pressure is 3.0 × 10 ⁻¹ atm. A GaN compound semiconductor crystal was grown for 300 minutes.
[0038]
Thereafter, it was cooled at a cooling rate of 5.3 ° C./min for 90 minutes to obtain a GaN compound semiconductor crystal having a film thickness of about 200 μm.
[0039]
When a GaN compound semiconductor crystal was grown using this substrate, the obtained GaN compound semiconductor crystal had an X-ray rocking curve half-width (FWHM) of 300 seconds, which was compared with the GaN compound semiconductor crystals of the above examples. The crystal quality was poor.
[0040]
Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the above embodiment. For example, the temperature of the substrate and the Ga raw material when adsorbing GaN atoms on the NdGaO ₃ substrate is not limited to the temperature applied in the above embodiment, so that the Ga temperature is 0.5 ° C. to 5 ° C. lower than the substrate temperature. Then, Ga atoms can be adsorbed on the substrate.
[0041]
In this embodiment, N ₂ is used as a carrier gas for supplying Ga atoms and NH ₃ onto the substrate in the step of forming the GaN thin film. However, H ₂ can be used instead of N ₂ . However, since nitride compounds are grown, it is desirable to use N ₂ as a carrier gas.
[0042]
Moreover, as growth conditions for the Ga compound semiconductor crystal, the GaCl partial pressure is 1.0 × 10 ^{−3 to} 1.0 × 10 ⁻² atm, and the NH ₃ partial pressure is 1.0 × 10 ^{−1 to} 4.0 ×. It is desirable that 10 ⁻¹ atm, the growth rate is 30 to 100 μm / h, the growth temperature is 930 to 1050 ° C., and the cooling rate is 4 to 10 ° C./min.
[0043]
【The invention's effect】
According to the present invention, in the method of growing a GaN-based compound semiconductor crystal on the surface (one main surface) of a rare earth 13 (3B) group perovskite crystal containing one or more rare earth elements as a substrate, the rare earth 13 ( 3B) A high quality GaN single crystal thin film having a uniform film thickness is obtained by performing a step of adsorbing Ga atoms on a group perovskite crystal substrate and a step of forming a GaN thin film by nitriding the adsorbed Ga atoms. Since the GaN thin film is formed, the possibility that the GaN thin film is adversely affected by the quality of the GaN-based compound semiconductor crystal grown thereon is reduced, and the crystal quality can be improved.

Claims (5)

In a method of growing a GaN-based compound semiconductor crystal on a surface of a rare earth 13 (3B) group perovskite crystal containing one or more rare earth elements as a substrate,
A step of adsorbing Ga atoms on the rare earth 13 (3B) group perovskite crystal substrate by introducing Ga atoms evaporated by heating Ga raw material onto the substrate with N ₂ gas ;
Subsequently, nitriding the adsorbed Ga atoms to form a GaN thin film;
Further, a step of growing a GaN-based compound semiconductor crystal on the GaN thin film,
A method for producing a GaN-based compound semiconductor crystal, comprising: The step of adsorbing Ga atoms on the rare earth 13 (3B) group perovskite crystal substrate lowers the temperature of the Ga raw material within a range of 0.5 ° C to 5 ° C from the temperature of the substrate. 2. A method for producing a GaN-based compound semiconductor crystal according to 1.   The said Ga atom is made to adsorb | suck to a board | substrate with the thickness of 1 molecular layer to several molecular layers, The said GaN thin film is formed with the thickness of 1 molecular layer to several molecular layers. The manufacturing method of GaN-type compound semiconductor crystal of description.   The 13 (3B) group element which comprises the said rare earth 13 (3B) group perovskite crystal | crystallization used as a board | substrate is at least 1 in Al, Ga, In, The Claims 1-3 characterized by the above-mentioned. The manufacturing method of the GaN-type compound semiconductor crystal in any one. 5. The method for producing a GaN-based compound semiconductor crystal according to claim 4, wherein the rare earth 13 (3B) group perovskite crystal is an NdGaO ₃ crystal.